During the manufacture of semiconductors, many different fluids must be precisely and accurately dispensed and deposited on the substrate being treated, such as deionized water, photoresist, spin on dielectrics, spin on glass, polyimides, developer and chemical mechanical polishing (CMP) slurries, to name a few. For example, in conventional apparatus for such applications, wafers to be processed are positioned beneath suitable nozzle that then dispenses a predetermined amount of liquid or slurry to coat or treat the wafer. The predetermined amount is premised on pump cycles, tubing diameters and other characteristics of the fluid containment environment, not only on the absolute amount or mass of fluid deposited on the wafer. Typically the wafer is then rotated to disperse the deposited liquid evenly over the entire surface of the wafer. It is readily apparent that the rate dispensing and the amount of liquid dispensed are critical in this process.
When fluid flow is stopped through the nozzle, such as between wafer treatments, the potential exists for droplets of liquid from the nozzle to form and fall onto the wafer positioned below the nozzle. This can destroy the pattern being formed on the wafer, requiring that the wafer be discarded or reprocessed. In order to avoid the formation of deleterious droplets on the nozzle, suckback or stop/suckback valves are commonly used. The latter of such valves are typically a dual pneumatically controlled valve pair, with one valve stopping the flow of liquid to the nozzle, and the other drawing the liquid back from the dispense end or outlet port of the nozzle. This not only helps prevent droplet formation and dripping at the port, but also helps prevent drying of the exposed surface of the liquid, which can lead to clogging of the nozzle, and reduces fluid contamination at the outlet.
The coating of larger wafers (e.g., 300 mm in diameter and larger) is also problematic, as turbulence issues arise. The rotational speed of the wafer is conventionally used to spread the coating fluid from the center of the wafer where it is applied, radially outwardly to the edge of the wafer. However, this approach creates turbulent airflow over the wafer and can result in uneven or nonuniform coatings. Reducing the spin speed with larger wafers reduces the turbulence at the surface of the wafer, but can introduce new problems. With the reduced speed, the fluid moves slower across the wafer, and thus spreading the fluid to the wafer edge before the fluid begins to setup or dry becomes an issue.
Pumps conventionally have been used to dispense liquids in semiconductor manufacturing operations. However, the pumps suitable for such applications are expensive and require frequent replacement due to excessive wear. In addition, the footprint of such pumps may be too large to be justified for all but the most demanding applications.
Liquid flow controllers such as the NT 6500 (Entegris Corp., Chaska, Minn.) are available that include differential pressure measurement, but they are not adaptable to a wide range of different flow rates and or viscosities. A modular solution to provide easily adjustable pressure drops is desirable.
It therefore would be desirable to provide a flow measurement and dispense system that results in precise, reproducible dispensing of fluid without the foregoing disadvantages. In addition, the present invention may be applied where precise control of fluid flow is desired or required.
It would be further desirable to provide a motorless pump system for accurate, repeatable dispensing of fluids.
It also would be desirable to provide a pneumatic proportional flow valve that is linear or substantially linear, exhibits minimal pressure drop, and exhibits minimal or no hysteresis.